You want to convert your .MOV files likely taken with your iPhone when the motion option was on, to still images. You scouted the web and you can't find a simple command on the thousands of ffmpeg options to do that.
You are not crazy, they don't have it! Not in a human feasible way. So here it is:
for i in *.mov; do ffmpeg -i "$i" -frames:v 1 png/"${i%.*}.png"; done
References
https://www.ostechnix.com/20-ffmpeg-commands-beginners/
https://stackoverflow.com/questions/5784661/how-do-you-convert-an-entire-directory-with-ffmpeg